Waveform generator producing output current variations as a function of predetermined input and control signal values

ABSTRACT

By deriving a substantially linear voltage signal from a pressure transducer and using that signal to control a plurality of current sources and current sinks, the controlled current may be passed through a resistance of known value to produce a usable output signal having a nonlinear relationship with respect to the pressure sensed by the transducer. If current sources to be controlled are designated by N, the resultant curve can have N-1 break points where the slope of the curve of output voltage with respect to sensed pressure changes.

United States Patent 1191 [111 3,873,855 Reddy 1451 Mar. 25, 1975 [54] WAVEFORM GENERATOR PRODUCING 3,247,397 4/1966 Kopek a a. 301/229 x OUTPUT CURRENT VARIATIONS AS A 3,430,616 3/1969 Glockler et a1. 123/119 FUNCTION OF PREDETERMINED INPUT 39 22;; AND CONTROL SIGNAL VALUES 3.560I727 2/1971 Schussler 1. 328/143 x [75] Inventor: Junuthula N. Reddy, Horseheads,

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: June 12, 1973 [21] Appl. No.: 384,481

Related US. Application Data [63] Continuation of Ser. No. 170,566, Aug. 10, 1971,

abandoned.

[52] US. Cl 307/260, 307/229, 307/235, 328/143, 123/32 EA [51] Int. Cl. H03k 4/00 [58] Field of Search 307/229, 260, 235;

[56] References Cited UNITED STATES PATENTS 3,157,873 11/1964 Slack 307/229 X Primary E.ratrziner.lohn S. Heyman Attorney, Agent, or Firm-Gerald K. Flagg {57] ABSTRACT By deriving a substantially linear voltage signal from a pressure transducer and using that signal to control a plurality of current sources and current sinks, the controlled current may be passed through a resistance of known value to produce a usable output signal having a nonlinear relationship with respect to the pressure sensed by the transducer. If current sources to be controlled are designated by N, the resultant curve can have N-l break points where the slope of the curve of output voltage with respect to sensed pressure changes.

11 Claims, 5 Drawing Figures I 158w 15BZ l l .l 1 J Y Tw x IY 1 PATENTED IIAR 2 5 I975 TIMING PICKUP Fl ECTRONIC CONTROL UNIT sum 1 n5 3 TEMPERATURE SENSOR BATTERY WAVEFORM GENERATOR PRODUCING OUTPUT CURRENT VARIATIONS AS A FUNCTION OF PREDETERMINED INPUT AND CONTROL SIGNAL VALUES This is a continuation of application Ser. No. 170,566, filed Aug. 10, 1971, now abandoned.

CROSS REFERENCE TO RELATED APPLICATIONS The instant application is related to commonly assigned co-pending applications bearing Ser. No. 170,565 issued as US. Pat. No. 3,765,380 on Oct. 16, 1973 for a Electronic Fuel Control System with Nonlinearizing Means Interconnectingthe Pressure Transducer with the Main Computation Means by Todd L. Rachel and to my commonly assigned co-pending application bearing Ser. No. 170,564 filed Oct. 10, 1971 and issued as US. Pat. No. 3,880,750 on Apr. 2, 1974 for a Apparatus for Providing a Nonlinear Pressure Transducer Output Signal.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of electronic fuel control systems for reciprocating piston internal combustion engines where the consumption of air by the engine constitutes an input parameter for the electronic fuel control system. More particularly, the present invention relates to that portion of the above described field in which the pressure of the air in the intake manifold is used as prime input parameter to determine the instantaneous fuel requirements for the associated engine. Specifically, the present invention relates to means for providing an electrical signal indicative of sensed pressure and representative of engine fuel requirements.

2. Description of the Prior Art The prior art teaches that in electronic fuel control systems for reciprocating piston internal combustion engines, various devices may be used to generate an electrical or electronic analog of the air pressure in the intake manifold of the engine. Such devices include inductive pressure transducers with an aneroid controlled movable core, capacitive pressure transducers with an aneroid controlled movable capacitive plate relationship and aneroid controlled rheostats or potentiometers. However, it is known that reciprocating piston internal combustion engines have a fuel requirement which does not relate in a linear fashion to the air pressure in the engine intake manifold. As a consequence, it has been necessary for the fuel control system designers to determine empirically the shape of the fuel requirement curve as a function of air pressure for a given engine and to thereafter suitably adapt one of the known pressure sensors to satisfy the empirically determined curve. Such solutions are complicated and expensive to implement. It is, therefore, an object of the present invention to provide a circuit forinterfacing between a known pressure sensor of simple and inexpensive construction and the main computing means to provide a suitably shaped curve of output signal chara further object of the present invention to provide such an interfacing circuit as may produce an output signal characteristic which changes slope frequently and which may go from negative to positive or from positive to negative slopes. Keeping the above objects in mind, it is a specific object of the present invention to provide an active circuit capable of satisfying the above enumerated objects.

As the art of electronics becomes more and more sophisticated, the cost of sensors required to produce an output which is nonlinearly related to input will begin to represent a more substantial percentage of the cost of the total system than is currently the case. It is. therefore, an object of the present invention to provide an electronic means to interface between a pressure transducer having a substantially linear response with response to variations in air pressure which circuitry may be fabricated in accord with the state of the art electronics to suitably nonlinearize the electrical signal produced by the pressure transducer.

The devices currently available in the prior art are furthermore handicapped in that they can only provide a very rough approximation to the desired electrical output for various air pressure inputs. It is, therefore, a further object of the present invention to provide an electronic interfacing network for coupling a resistive aneroid type pressure transducer to the main computing portion of an electronic fuel control system capable of providing an electrical response which is nonlinear with respect to variations in the air pressure in the in take manifold. It is a more specific object of the present invention to provide such an interfacing network capable of providing an output electrical curve having a plurality of points at which the slope of the curve may change. It is a still more specific object of the present invention to provide an active electronic interfacing network which produces a voltage output signal which is nonlinearly related to a voltage input signal having a substantially linear relationship with respect to variations in air pressure in the intake manifold of the associated engine. It is a specific object of the present invention to provide an electronic interfacing network comprised of a plurality of current generating means which may be serially controlled to provide, at a reference location, an electrical current having a magnitude which is a non-linear function of air pressure in the intake manifold.

SUMMARY OF THE PRESENT INVENTION The present invention contemplates generating a voltage signal which is approximately linearly related to the pressure in the air intake manifold and using this signal to control a plurality of current generating means which are serially arranged to be variably operative over selected ranges of air intake manifold pressure. The present invention further contemplates combining the currents generated thereby into a single current which is dissipated through a fixed resistor wherein the voltage drop across the fixed resistor constitutes the output signal.

An additional aspect of the present invention resides in the provision of at least one current sink means to provide an additional source of variation in the current to be dissipated by the fixed resistance.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a schematic diagram of an electronic fuel control system which may utilize the present invention.

FIG. 2 shows a block diagram representation of the electronic control unit of FIG. 1.

FIG. 3 shows a schematic circuit diagram of an input transducer nonlinearizing circuit according to one embodiment of the present invention.

FIG. 4 shows a graph of current with respect to pressure for the various components of the circuit of FIG. 3.

FIG. 5 shows a graph of the output current of the circuit of FIG. 3 with respect to pressure. This graph is the summation of the FIG. 4 graphs.

DETAILED DESCRIPTION OF THE DRAWING Referring now to FIG. 1, an electronic fuel control system is shown in schematic form. The system is comprised of a main computing means or electronic control unit 10, a manifold pressure sensor 12, a temperature sensor 14, an input timing means 16 and various other sensors denoted as 18. The manifold pressure sensor 12 and the associated other sensors 18 are mounted on throttle body 20. The output of the computing means is coupled to an electromagnetic injector valve member 22 mounted in intake manifold 24 and arranged to provide fuel from tank 26 via pumping means 28 and suitable fuel conduits 30 for delivery to a combustion cylinder 32 of an internal combustion engine otherwise not shown. While the injector valve member 22 is illustrated as delivering a spray of fuel towards an open intake valve 34, it will be understood that this representation is merely illustrative and that other delivery arrangements are known and utilized. Furthermore, it is well known in the art of electronic fuel control systems that computing means 10 may control an injector valve means comprised of one or more injector valve members 22 arranged to be actuated singly or in groups of varying numbers in a sequential fashion as well as simultaneously. The computing means is shown as energized by battery 36 which could be a vehicle battery and/or battery charging system as well as a separate battery.

The logic diagram shown in FIG. 2 illustrates the computing means 10 in a nonparticularized manner as applied to two-group injection the elements illustrated in the logic diagram of FIG. 2 being of the type generally corresponding for example with those shown in FIG. 2 and described in' greater detail with respect to FIG. 4 of commonly-assigned U.S. Pat. No. 3,763,833 expressly incorporated herein by reference, this patent being issued to T. L. Rachel on Oct. 9, 1973 on an application claiming the benefit of an Apr. 14, 1969 filing date. In FIG. 2, there is shown a switching device 38 capable of producing alternating output signals and receiving as input a signal or signals representative of engine crank angle as from sensor 16. Mechanically, sensor 16 could be a single lobed cam, driven by the engine and alternately opening and closing a pair of contacts. Since this arrangement could generate spurious signals, as by contact bounce, the switching device 38 will be described and discussed as a flip flop since the flip flop is known to produce a substantially constant level of output at one output location and zero level at the other output location in response to a triggering signal which need only be a spike input but may also be of longer duration and a flip flop may be readily made insensitive to other types of signals. Traces 1 and 2 illustrate the alternating triggering input signals while traces 3 and 4 illustrate the time relationship of the two output signals. Signals received on the nontriggering input will, of course, have no effect on a flip flop. Outputs 40 and 42 are connected to the inputs of a logic gate 44 which may for example correspond to AND gate 220 having capacitor coupled inputs as shown in and described in greater detail with respect to FIG. 4 of the hereinabove cited U.S. Pat. No. 3,763,833. Gate 44 is arranged to give a relatively short duration pulse whenever the flip flop 38 changes state and to produce a constant level d.c. output at all other times. Outputs 40 and 42 are also connected to the inputs of a pair of AND gates with output 40 being connected to one input of AND gate 46 and the output 42 being connected to one input of AND gate 48. The output of the gate 44 is connected to the input of an adaptive delay means 50 which may for example correspond with adaptive delay 26 shown in and described in greater detail with respect to FIG. 4 in the hereinabove cited U.S. Pat. No. 3,763,833 and which receives, as control inputs, signals from the various engine parameter sensors, as at 52, indicative of engine operating conditions and, therefore, of the engine fuel requirement. As will be readily observed, one of the inputs at 52 is derived from signal generator 54 which receives, as its input, the signal 9 derived from the pressure sensor 12 of FIG. 1 and representative of the instantaneous manifold pressure. Since, according to this invention, pressure sensor 12 may be a simple potentiometer having a substantially linear response with respect to pressure, the derived output signal, which may be a voltage, V is expressed herein in terms of 6, the angular movement of the slider element of a potentiometer or in terms of V the actual electrical output signal. The output of theadaptive delay means 50 is fed through an inverter 56 and the output of the inverter 56 is connected to a second input of each AND gate 46 and 48. The output of AND gate 46 is connected to amplifier 58 which, in turn, supplies controlling current to the first injector group. AND gate 48 is connected to amplifier 60 which supplies controlling current to the second injector group.

As will be readily apparent, the presence of an output signal from the flip flop 38 will occur at one output location to the exclusion of the other. This signal will then appear at one input of only one AND gate of only one amplifier. This signal selectively designates an injector or injector group for imminent injection. For the sake of example, we shall assume that the output signal of the flip flop 38 is at output location 40 so that the signal also appears at one input of AND gate 46. The signal from the output 40 of the flip flop 38 also appears at the gate 44 where, assuming the flip flop 38 has just changed state, a short duration signal is passed to the adaptive delay means 50. The adaptive delay means 50 is operative to produce an output after the passage of a predetermined amount of time. This time is determined by the values of the various sensory inputs applied at 52 to the adaptive delay 50. During this initial period of time when the output of the adaptive delay 50 is zero, the inverter 56 is producing a full-strength output signal. The details of adaptive delay means 50 may be seen in U.S. Pat. No. 3,763,833. This signal is applied to one input of each of the AND gates 46 and 48. Because of the intrinsic nature of AND gates, an output signal is produced only while an input signal is being applied to each and every'input. This then dictates that AND gate 46- will produce an output to be amplified by amplifier 58 to open the first injector group since it is receiving an injector selection command directly from the flip flop 38 and an injector control command from the inverter 56. At the end of the time delay period, adaptive delay means 50 produces a signal which is then inverted from a positive signal to a zero level signal by the inverter 56 so that the injection control command output signal of the inverter 56 is removed from the input to the AND gate 46 and the output of the AND gate 46 goes to zero thereby allowing the first injector group to close. During the period of time the first injector group is open, a metered amount of fuel under pressure is injected by the first injector group.

Referring now to FIG. 3, signal generator 54 according to the present invention is illustrated in FIG. 2 in a preferred embodiment. Signal generator 54 is comprised essentially of a means for receiving an input signal indicative of intake manifold pressure as illustrated at 6, V a plurality of current generating means illustrated in dashed boxes A, B, C, D and E and a means for converting a current signal into a voltage signal illustrated as resistor 100. In addition, a plurality of current sink means are illustrated in dashed lined boxes V, W, X, Y, and Z. The current sinks represent optional additive portions of signal generator. 54. For purposes of illustration, a current sink X is shown operatively coupled to current generator'C while current sinks V, W, Y, and Z are shown inoperative. Depending upon the desired shape of the output voltage (or current) curve with respect to pressure'variations, current sinks V, W, Y and Z may or may not be included and current sink X may be excluded. For purposes of the herein discussion, current generator C and current sink X will be described in detail. It should be noted at this'time that the various elements within current generator C and current sink X are described with a suffix letter C or X. Similar elements in the other current generators and current sinks are denoted by similar numerals carrying the appropriate suffix to indicate the particular current generator or current sink in which they are operative.

Circuit 54 is further illustrated as including a constant current generator 102 which is operative to provide. for level shifting of the final output curve. Constant current generator 102 is also not considered to be essential to the present invention. An isolating transistor 104 is shown interconnecting the input signal V to each of the current generating means, A, B, C, D, E. This transistor is operative to shield the actual sensor element from any loading effects which might be presented by the circuit 54. The entire circuit 54 is shown as energized by voltage B+ as illustrated at the. various locations so noted and B+ may represent the vehicle battery and/or battery charging system of thevehicle, or it may also represent an independent supply of voltage. As is well understood in the art, the designation 8+ is not to be considered limiting to a positive voltage potential but is merely indicative of a potential difference between the location, denoted 8+ and the various locations denoted as ground.

Current generating means C is comprised of an input transistor 106C, a pair of generator transistors 108C and 110C, a feedback transistor 112C, a load resistor 114C and various voltage and current level establishing resistors 116C, 118C and 120C. The emitter of the input transistor 106C is coupled to circuit location 122C as is the base of generator transistor C. Circuit location 122C is also coupled directly to the emitter of the following current generator means D feedback transistor ll2D. So long as the input voltage V is less than a pre-established value determined by feedback transistor 112D, the voltage appearing at the base of transistor 110C will be at a constant value determined by feedback transistor 112D. The voltage at the emitter of transistor 110C will be the voltage at the base thereof increased by the emitter-base voltage differential. The voltage at the base of transistor 108C is determined by the voltage divider effect of resistors 116C and 118C and the voltage appearing at the emitter of transistor 108C will be the base voltage thereof less the emitter-base voltage differential. The current flowing through current level establishing resistor C will be the voltage differential appearing across resistor 120C divided by the resistive value thereof. This current will flow through transistor 110C and will be present, substantially unchanged, in output conductor 126C. Thevoltage appearing at the emitter of feedback transistor 112C will be determined bythe voltage at the base of transistor 108C reduced by two emitter-base junction voltage drops and will be communicated to circuit location 1228.

When the input voltage signal V rises above the feedback voltage by an amount sufficient to overcome the various emitter-base junction voltage drops, the voltage at circuit location 122C will begin to rise following V This increase will be communicated to the emitter of transistor 110C where the voltage differential across resistor 120Cwill begin to diminish. This will reduce the amount of current flowing through resistor 120C and concomitantly, the amount of current flowing in conductor 126C. Since the voltage at the emitter of transistor 108C is substantially a constant value, variations in the voltage at the emitters of transistor 110C will directly affect the value of current generated. The voltage at the emitter oftransistor 110C will follow the voltage at the base thereof (and V until the voltage at the emitter of transistor 110C equals the voltage at the emitter of transistor 108C. Thereafter, the emitterbase junction of transistor 110C will be reverse biased and transistor 110C will be switched off.

It will be observed that current generating means A does not include a feedback resistor and that current generating means E includes a resistance 124E going to B+ in place of a connection to a feedback resistor in a succeeding current generating means stage. These differences occur because, as is obvious, there is no current generating means which precedes A and there is a similar lack of current generating means which succeeds E. In current generating means E, the presence of resistance 124 going to 8+ as illustrated, supplants the need for feedback which is provided in the other current generating means stages. Feedback is used to provide that the end of one selected operational region of pressure variations corresponds to the beginning of the next selected operational region. As such, current generating means A and E have only one critical point each, while current generating means B, C and D have two critical points each.

Each of the current generating means A, B, C, D and E produces an output current in output conductor 126. In current generating means A, B, D and E, this conductor 126 is connected to common branch 128 which communicates with output resistor 100 and circuit output port 130. The current generated by those current generating means coupled to common conductor 128 will be dissipated through output resistor 100 and the voltage appearing at output circuit 130, with respect to ground, will represent the nonlinearized output signal as a function of intake manifold air pressure.

Current generating means C output conductor 126C is coupled to current sink means X at input location 150. The current generated by generating means C will flow into the base of transistor 152X and into the base of transistor 154X through resistor 156X. The collector of transistor 154X is connected to 8+ as shown through resistance 158X. The collector of transistor 152X is connected to common conductor 128 and the emitter of transistor 152X is connected through resistance 160X to ground. Depending on the magnitude of the current being generated by current generating means C, and further depending upon the magnitude of resistance I60X, the amount of current being drawn out of the output conductor 128 will be determined. This current will be subtracted from the total amount flowing through output conductor 128 and output resistance 100 so that the output signal appearing at output port 130 will be decreased. As soon as the output current of current generating means C begins to decrease in the previously described fashion, the amount of current being drawn out of, or subtracted from, the current flowing in output conductor 128 will have a similar decrease and the output signal appearing at output port 130 will tend to decrease.

In the event that the output signal appearing at circuit output port 130 is to have a minimum value which may or may not be constant over a specified range, current generating means 102 is illustrated to provide to output resistance 100 a fixed magnitude of current through current generating transistor 180 and resistance 182. Transistor 180 is controlled by control transistor 184 which is held in constant conduction mode by resistances 186, 188 and 190.

Referring now to FIG. 4, a graph of current with respect to manifold pressure and with respect to input voltage signal is plotted showing the individual currents for each current source. The graphs are alphabetically labeled to represent each of the current generators according to the designations of FIG. 3. The effect of the current sinks has not been plotted. However, the effect of activating a current sink would be (graphically) to include a curve representing negative current having constant and variable regions similar in extent to that of the associated current generating means but having a magnitude which may be greater or lesser than the magnitude of the generated current at any given input voltage or manifold pressure depending upon the values of resistances 156 and 160. The horizontal axis is labeled in terms of pressure and numerically in millimeters of mercury. As will be observed, the currents being individually generated have variable portions which occur only over selected regions of pressure variation. For example, graph C (the current generated by current generating means C) varies from a maximum value to a minimum value for pressure variations between 550 and 450 millimeters of mercury. The regions variation of current may be selected to overlap or to be nonoverlapping as illustrated.

Referring now to FIG. 5, the various graphs of FIG. 4 are shown added to produce the composite curve F as illustrated. The vertical axis is labeled in terms of current and in terms of output voltage detected across the output resistor. As can be seen, the curve F includes 4 knees, or break points, at which the slope of the curve changes. This curve represents the analog of engine fuel requirements with respect to air intake manifold pressure and the various curves, A, B, C, D and E are calculated to produce a curve F which matches as closely as possible the empirically derived curve of actual engine fuel requirement with respect to manifold air pressure.

The present invention contemplates relatively smooth transitions between different operational regions and to insure uniformity of region changeovers, feedback transistor 112 establishes the end of one variable region at the value of the beginning of the next. Precisely sized resistors could also perform the same function. In those instances where large discontinuities are desired, the informational feedback may be dis torted to provide a positive or negative spike" of variation.

The present invention thus clearly satisfies the stated objectives in the form of the preferred embodiment as well as in those variations within the skill of the man of ordinary skill in the art. The current sinks, for example, may be controlled as shown by connecting selected current generating means to the current sinks instead of to the output resistance or in the alternative, may be directly controlled by the input signal to be selectively active over specific regions of intake manifold air pressure. The specific form of the various sources and sinks as well as the total number thereof may also vary.

I claim:

1. A circuit for providing a shaped output signal in response to variations in the magnitude of an input signal comprising:

means for providing first, second, and third control signals, said second control signal having a magnitude intermediate the magnitude of said first and third control signals; first signal generating means responsive to the input signal and the control signals for providing a first output signal having a value that varies in response to input signal variations only between first and second predetermined values determined by the values of said first and second control signals;

second signal generating means coupled to receive the input signal and said second and third control signals for providing a second output signal having a value that varies in response to input signal variations only between said second predetermined value and a third predetermined value determined by the value of said third control signal; and

means for combining the output signals to provide a resultant signal having a shape determined by the values of the control signals and variations of the input signal.

2. The circuit of claim 1 in which said first signal generating means comprise:

conductive path means including a resistor;

first arid second signal generating transistor means responsive to said first and second control signals respectively for providing a signal differential across said resistor, said differential having a value determined by the values of said first and second control signals and producing an output signal in said conductive path; and

input transistor means responsive to the input signal and to said first control signal for applying input signal values having a predetermined relationship with respect to the value of said first control signal to said first signal generating transistor means to thereby vary the signal differential across said resistor.

3. The circuit of claim 2 in which:

said second signal generating means include:

second conductive path means including a second resistor;

third and fourth signal generating transistor means responsive to said second and third control signals respectively for providing a signal difference across said second resistor determined by the values of said second and third control signals, the value of said signal difference across said second resistor determining the value of said second output signal provided by the second signal generating means; and

second input transistor means responsive to the input signal and to said second control signal for applying input signal values having a predetermined relationship with respect to said second control signal to said third signal generating transistor means to vary the signal difference across said second resistor.

4. The circuit of claim 3 in which:

said third control signal has a value greater than said second control signal, said second control signal has a value greater than said third control signal;

said input transistor means comprise means for applying only those input signal values greater than said first control signal to said first signal generating transistor means to reduce the signal differential across said resistor; and

said second input transistor means comprise means for applying only those input signal values greater than said second control signal to said third signal generating transistor means to reduce the signal difference across said second resistor.

5. The circuit of claim 4 further including feedback transistor means intermediate the second control signal providing means and said second input transistor means for preventing input signal values applied by said second input transistor means to. said third signal generating transistor means from altering the value of the signal difference provided across said first resistor.

6. The circuit of claim 1 further including:

an energy draining subsection connected to said combining means and switchingly connected to said first and second signal generating means for draining energy from said combining means in proportion to the value of signals received from said first and second signal generating means.

7. A circuit for generating an output waveform varying with the magnitude of an engine operating parameter signal provided by engine operating parameter signaling means, said waveform generating circuit comprising:

a. first and second sources of constant reference potential;

b. first and second waveform generating means each comprising:

i. first control voltage generating means comprising first control impedance means and first control voltage coupling means, said first control voltage coupling means being coupled to said first source of constant reference potential and said first control impedance means for cooperating with said first control voltage impedance means to provide a first control voltage;

ii. second control voltage generating means comprising second control voltage impedance means coupled to said second source of constant reference potential, second control voltage coupling means coupled to said second control voltage impedance means, and parameter signal coupling means coupled to said second control voltage coupling means and said engine operating parameter signaling means, said parameter signal coupling means operative to couple said engine operating parameter signal to said second control voltage coupling means only when the magnitude of said parameter signal exceeds a first predetermined magnitude, said second control voltage coupling means operative to provide a second control voltage which is a second constant control voltage less than said first constant control voltage only when the magnitude of said engine operating parameter is less than said first predetermined magnitude, which varies between said first and second constant control voltages as the magnitude of said engine operating parameter signal varies between said first predetermined magnitude and a second predetermined magnitude greater than said first predetermined magnitude, and which substantially equals said first control voltage as long as said magnitude of said engine operating parameter exceeds said second predetermined magnitude, said first predetermined magnitude of said first waveform generating means being less than said first predetermined magnitude of said second waveform generating means and said second predetermined magnitude of said first waveform generating means being substantially equal to said first predetermined magnitude of said second waveform generating means, and I iii. output impedance means having first and second ends respectively coupled to said first and second control voltage coupling means, said output impedance means cooperating with said first and second control voltage coupling means to provide an output current varying with the difference between said first and second control voltages, said output current varying towards a constant current level only when the magnitude of said operating parameter signal exceeds said first predetermined magnitude and remaining at said constant current level as long as the magnitude of said engine operating parameter signal exceeds said second predetermined magnitude;

c. output waveform generating means coupled to each said second control voltage coupling means for combining said output currents of said first and second waveform generating means to provide said output waveform; and

(1. feedback means coupling said first control voltage coupling means of said first waveform generating means and said second control voltage coupling means of said second waveform generating means for holding said second control voltage of said second waveform generating means substantially equal to said first control voltage of said first waveform generating means when the magnitude of said engine operating parameter is less than said first predetermined magnitude of said first waveform generating means,

whereby said output current of said second waveform generating means begins to vary towards said constant current level only after the magnitude of said engine operating parameter signal exceeds said second predetermined magnitude of said first waveform generating means so that said output current of just one of said first and second signal generating means varies when the magnitude of said engine operating parameter varies.

8. The circuit of claim 7 wherein at least one of said first and second control voltage coupling means comprises a transistor having an electrode coupled to one of said first and second ends of said output impedance means.

9. The circuit of claim 8 wherein at least one of said parameter signal coupling means and said feedback means comprises a transistor having an electrode coupled to said second control voltage impedance means.

10. The circuit of claim 9 wherein each of said transistors has a second electrode and has a predetermined voltage drop between said first and second electrodes when conducting, said predetermined voltage drop causing said output current of said first waveform generating means to equal said constant current level at substantially-the same magnitude of said engine operating parameter signal as that at which said output current of said second waveform generating means begins to vary towards said constant current level.

11. The circuit of claim 7 wherein said first and second control voltage coupling means, said feedback means and said parameters signal coupling means each comprise a transistor having first and second electrodes and a predetermined voltage drop therebetween when conducting said predetermined voltage drop causing said output current of said first waveform generating means to equal said constant current level at substantially the same magnitude of said engine operating parameter signal as that at which said output current of said second waveform generating means begins to vary towards said constant current level. 

1. A circuit for providing a shaped output signal in response to variations in the magnitude of an input signal comprising: means for providing first, second, and third control signals, said second control signal having a magnitude intermediate the magnitude of said first and third control signals; first signal generating means responsive to the input signal and the control signals for providing a first output signal having a value that varies In response to input signal variations only between first and second predetermined values determined by the values of said first and second control signals; second signal generating means coupled to receive the input signal and said second and third control signals for providing a second output signal having a value that varies in response to input signal variations only between said second predetermined value and a third predetermined value determined by the value of said third control signal; and means for combining the output signals to provide a resultant signal having a shape determined by the values of the control signals and variations of the input signal.
 2. The circuit of claim 1 in which said first signal generating means comprise: conductive path means including a resistor; first and second signal generating transistor means responsive to said first and second control signals respectively for providing a signal differential across said resistor, said differential having a value determined by the values of said first and second control signals and producing an output signal in said conductive path; and input transistor means responsive to the input signal and to said first control signal for applying input signal values having a predetermined relationship with respect to the value of said first control signal to said first signal generating transistor means to thereby vary the signal differential across said resistor.
 3. The circuit of claim 2 in which: said second signal generating means include: second conductive path means including a second resistor; third and fourth signal generating transistor means responsive to said second and third control signals respectively for providing a signal difference across said second resistor determined by the values of said second and third control signals, the value of said signal difference across said second resistor determining the value of said second output signal provided by the second signal generating means; and second input transistor means responsive to the input signal and to said second control signal for applying input signal values having a predetermined relationship with respect to said second control signal to said third signal generating transistor means to vary the signal difference across said second resistor.
 4. The circuit of claim 3 in which: said third control signal has a value greater than said second control signal, said second control signal has a value greater than said third control signal; said input transistor means comprise means for applying only those input signal values greater than said first control signal to said first signal generating transistor means to reduce the signal differential across said resistor; and said second input transistor means comprise means for applying only those input signal values greater than said second control signal to said third signal generating transistor means to reduce the signal difference across said second resistor.
 5. The circuit of claim 4 further including feedback transistor means intermediate the second control signal providing means and said second input transistor means for preventing input signal values applied by said second input transistor means to said third signal generating transistor means from altering the value of the signal difference provided across said first resistor.
 6. The circuit of claim 1 further including: an energy draining subsection connected to said combining means and switchingly connected to said first and second signal generating means for draining energy from said combining means in proportion to the value of signals received from said first and second signal generating means.
 7. A circuit for generating an output waveform varying with the magnitude of an engine operating parameter signal provided by engine operating parameter signaling means, said waveform generating circuit comprising: a. first and second sources of constant referEnce potential; b. first and second waveform generating means each comprising: i. first control voltage generating means comprising first control impedance means and first control voltage coupling means, said first control voltage coupling means being coupled to said first source of constant reference potential and said first control impedance means for cooperating with said first control voltage impedance means to provide a first control voltage; ii. second control voltage generating means comprising second control voltage impedance means coupled to said second source of constant reference potential, second control voltage coupling means coupled to said second control voltage impedance means, and parameter signal coupling means coupled to said second control voltage coupling means and said engine operating parameter signaling means, said parameter signal coupling means operative to couple said engine operating parameter signal to said second control voltage coupling means only when the magnitude of said parameter signal exceeds a first predetermined magnitude, said second control voltage coupling means operative to provide a second control voltage which is a second constant control voltage less than said first constant control voltage only when the magnitude of said engine operating parameter is less than said first predetermined magnitude, which varies between said first and second constant control voltages as the magnitude of said engine operating parameter signal varies between said first predetermined magnitude and a second predetermined magnitude greater than said first predetermined magnitude, and which substantially equals said first control voltage as long as said magnitude of said engine operating parameter exceeds said second predetermined magnitude, said first predetermined magnitude of said first waveform generating means being less than said first predetermined magnitude of said second waveform generating means and said second predetermined magnitude of said first waveform generating means being substantially equal to said first predetermined magnitude of said second waveform generating means, and iii. output impedance means having first and second ends respectively coupled to said first and second control voltage coupling means, said output impedance means cooperating with said first and second control voltage coupling means to provide an output current varying with the difference between said first and second control voltages, said output current varying towards a constant current level only when the magnitude of said operating parameter signal exceeds said first predetermined magnitude and remaining at said constant current level as long as the magnitude of said engine operating parameter signal exceeds said second predetermined magnitude; c. output waveform generating means coupled to each said second control voltage coupling means for combining said output currents of said first and second waveform generating means to provide said output waveform; and d. feedback means coupling said first control voltage coupling means of said first waveform generating means and said second control voltage coupling means of said second waveform generating means for holding said second control voltage of said second waveform generating means substantially equal to said first control voltage of said first waveform generating means when the magnitude of said engine operating parameter is less than said first predetermined magnitude of said first waveform generating means, whereby said output current of said second waveform generating means begins to vary towards said constant current level only after the magnitude of said engine operating parameter signal exceeds said second predetermined magnitude of said first waveform generating means so that said output current of just one of said first and second signal generating means varies when the magnitude of said engine operating parameter varies.
 8. The circuit of claim 7 wherein at least one of saiD first and second control voltage coupling means comprises a transistor having an electrode coupled to one of said first and second ends of said output impedance means.
 9. The circuit of claim 8 wherein at least one of said parameter signal coupling means and said feedback means comprises a transistor having an electrode coupled to said second control voltage impedance means.
 10. The circuit of claim 9 wherein each of said transistors has a second electrode and has a predetermined voltage drop between said first and second electrodes when conducting, said predetermined voltage drop causing said output current of said first waveform generating means to equal said constant current level at substantially the same magnitude of said engine operating parameter signal as that at which said output current of said second waveform generating means begins to vary towards said constant current level.
 11. The circuit of claim 7 wherein said first and second control voltage coupling means, said feedback means and said parameters signal coupling means each comprise a transistor having first and second electrodes and a predetermined voltage drop therebetween when conducting said predetermined voltage drop causing said output current of said first waveform generating means to equal said constant current level at substantially the same magnitude of said engine operating parameter signal as that at which said output current of said second waveform generating means begins to vary towards said constant current level. 